As described in Wolinsky U.S Pat. No. 4,824,436, the process of treating coronary artery disease with an balloon (typically the PTCA procedure) results in at least a temporary, forcible expansion of a coronary artery cross section which is narrowed by an atherosclerotic lesion or stenosis. However, following such rough, physical balloon expansion of such a stenosis, often a restenosis takes place in which the artery again closes up. To counter this, heparin is given to the patient. For example, it is the current custom in a PTCA procedure to deliver by injection up to about 10,000 units of heparin as a bolus during or immediately after the procedure, with hourly, additional doses of heparin being administered up to 24 hours after the PTCA procedure. This, however, has known disadvantages in that some patients such as ulcer patients or patients with high blood pressure are contraindicated for the administration of such large amounts of heparin.
As another approach to the problem of restenosis, the previously cited Wolinsky patent teaches the administration of heparin by means of a special catheter to the stenosis area after a PTCA procedure or the like. However, this requires the insertion of a second catheter into the patient's arterial system, to accomplish this special application of heparin
In Rowe pending U.S. Pat. Application No. 322,929, filed Mar. 14, 1989 and entitled Method and Apparatus for Delivery of Therapeutic Agent, a balloon catheter is described, being, if desired, of a type useful for a PTCA or related procedure. However, as an improvement, a coating of heparin or other medication is carried on the surface of the balloon. Accordingly, heparin or other medication is forced into the stenosis site by the pressure of the expanding balloon, so that the heparin is applied in a single step as the stenosis area is physically expanded by the balloon. However, there may be a need for larger quantities of medication than can be provided by such an expansion balloon surface as described in the above-mentioned patent application. Additionally, there may be a need for a sequence of medications, to be applied one after the other, and this also is not readily accomplished in the cited patent application with a single catheter insertion. Additionally, it may be desired to apply the medication without the application of substantial pressure, and this also is not done with ease in the above-described invention. Also, there is a need for a system in which the medication does not leak out of the system until the catheter is positioned at exactly the desired location, and where the choice of medication may change with a late decision by the physician after the catheter has been emplaced.
By the invention of this application, any or all of the above objectives may be accomplished, to provide greater flexibility and effectiveness to catheters for delivering therapeutic agents.